Text enhanced telephony

ABSTRACT

A system is described for assisting the hard of hearing in the use of the telephone, the system termed here text enhanced telephony or TET. The hard of hearing user uses a TET device or appliance which permits the user to speak and to hear the words spoken by the other party, the TET device also supplying to the user a text character stream of the words spoken by the other party. The TET system uses the system of voice-to-text relays, already in existence to assist the deaf community communicate with hearing persons over the telephone, to translate the spoken voice into a text stream. The TET relay and TET device are capable of separating voice and digital communications frequencies carrying text so that voice and a text communications stream of the words spoken by the voice can be carried over a common telephone line. The devices can also be capable of automated capabilities such that the devices can automatically configure a three-party relay call without the need for the user&#39;s instructions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 07/842,943 filedJan. 9, 1992, now U.S. Pat. No. 5,351,288, which was acontinuation-in-part of Ser. No. 07/616,720 filed Nov. 16, 1990, nowU.S. Pat. No. 5,081,673, which was a continuation of Ser. No. 07/255,357filed Oct. 11, 1988, now abandoned. This application is also acontinuation-in-part of Ser. No. 08/129,894, filed Sep. 30, 1993 and ofSer. No. 08/155,061 filed Nov. 19, 1993, both of which arecontinuations-in-part of Ser. No. 07/886,552 filed May 20 1992, nowabandoned.

FIELD OF THE INVENTION

The present invention relates to telephone communication in general andrelates in particular, to assisted telephone communication for personshaving attenuated hearing capability.

BACKGROUND OF THE INVENTION

Much of modern personal communication, both in social and businessenvironments, takes place through the telephone. Yet, there are manypersons in society who have attenuated hearing capability and are thusdisabled or incapable or handicapped in using the voice telephone systemcommonly in use today. For person who are deaf, there has for some timebeen a system of communication through the telephone system which hasbeen used by the deaf community. That system makes use of devices knownas telecommunication devices for the deaf (TDDs), also known as texttelephones (TTYs). Current TDDs are electronic devices consisting of akeyboard and a display and a modem, to acoustically or directly coupleto a telephone line, which permit the user to type characters into theirkeyboard, with the characters then be encoded and transmitted over thetelephone line to be displayed on the display of a communicating orremote TDD.

Current TDD communication is conducted in a code, known as Baudot orBaudot/Weitbrecht, which evolved historically at a time when manytelecommunication devices for the deaf were based on mechanical orelectromechanical devices rather than the current generation ofelectronic devices. Accordingly, the Baudot protocol was constructed fora set of constraints which are no longer relevant to present daydevices. The original Baudot protocol was a uni-directional, or simplex,system of communication conducted at 45.5 baud. The normal Baudotcharacter set consists of a 5 bit characters, and the system is abi-tonal system based on 1400 and 1800 hertz tones. The protocol doesnot utilize a carrier when no signals are being sent, and because of theprotocol for character transmission, which includes a start bit and atleast 11/2 stop bits, it is only possible to send approximately 6characters per second, one way, during conventional Baudotcommunications.

In spite of its limitations, the Baudot communication system, and TDDs,are widely used within the community of persons who are deaf. Inaddition, systems have been implemented to permit users of the TDDsystem to communication with hearing people. This is done through theuse of a so-called "relay." A relay, as used herein, refers to a systemof voice to TDD communication which uses an operator referred to as acall assistant who serves as an intermediate between a hearing user onone telephone line and a deaf TDD user on a second telephone line. Thecall assistant wears a headset to communicate by voice with the hearinguser and also has access So a TDD so that the call assistant cancommunicate with the deaf user via the TDD. Thus, the call assistantserves as an intermediary between the deaf person and the hearing personso as to, in effect, translate from voice to digital electronic forms ofcommunication.

While the TDD communication system has a constituency within the deafcommunity, it is not widely used by persons who are deficient in hearingcapability, but would not describe themselves as deaf. Many otherwisefully able persons, particularly elderly ones, suffer attenuated hearingcapability due to aging, disease, or other traumatic condition. Manypersons who have some degree of hearing capability left do not considerthemselves "deaf," and therefore will tend not to avail themselves ofspecialized equipment intended for the deaf community. If a person hasspent much of his or her life engaged in oral communication using thespoken word in the telephone, it is difficult to accept that telephoniccommunication may become difficult or impractical as one's hearingdeclines in efficiency. No system has heretofore existed which iscapable of assisting the person who has significant hearing loss, incommunication over the telephone in a manner which emulates, to thefullest extent possible, the normal telephonic communication patterns ofhearing people.

SUMMARY OF THE INVENTION

The present invention is summarized in that a text enhanced telephonicdevice is made available to persons who have a hearing loss. The textenhanced telephone will, to the user, operate like a normal telephonebut will, in addition to receiving normal voice communication, permitthe user to receive the words spoken by the remote party in a visualformat on a visual display located on the text enhanced telephone whichthe user is operating.

It is an object of the present invention to provide a text enhancedtelephone which may be operated by a user who is hearing deficient in amanner like all conventional telephones, but with the added capabilitythat received communications are displayed in text so that the user canread the communications to supplement any words which are not understoodverbally.

It is a feature of the present invention that the operation of the textenhanced telephone can be made transparent to the user so that little orno retraining or otherwise adaptive behavior needs to be taught to theuser of the system.

Other objects, advantages, and features of the present invention willbecome apparent from the following specification when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of one embodiment of a textenhanced telephone (TET) constructed in accordance with the presentinvention.

FIG. 2 is a schematic illustration of the operation of a conventionalTDD relay.

FIG. 3 is a schematic illustration of the operation of a TDD relay withvoice carry-over.

FIG. 4 is a schematic illustration of the operation of a text enhancedtelephone (TET) relay system.

FIG. 5 is a circuit diagram of a TET relay for use in the system of FIG.4.

FIG. 6 is a timing diagram of synchronization sequences for use in anenhanced TDD protocol useful in the present invention.

FIG. 7 is a circuit diagram of a notch filter useful in a TET device.

FIG. 8 is a circuit diagram of another embodiment of a notch filterwhich can be used in a TET device.

FIG. 9 is a circuit diagram of another embodiment of a TET device.

FIG. 10 is an exterior view of another embodiment of a TET device.

FIG. 11 is a circuit diagram of an alternative relay circuit.

FIG. 12 is a circuit diagram of another alternative relay system.

DESCRIPTION OF THE INVENTION

The present invention envisions a new class of telephone communicationsequipment, here termed text enhanced telephones or TETs. These TETdevices are intended to assist the hard of hearing person in the use ofa telephone to communicate with others in a normal fashion. The textenhanced telephone device can be packaged in any of several ways. Thedevice can be, for example, any of (i) an intermediate appliance pluggedin between the handset and the telephone base, (ii) an intermediateappliance plugged in between the telephone and the wall jack or (iii) aunitary device built into the telephone itself. Whichever physical formit takes, the TET device includes a visual display onto which textcharacters may be displayed. The user of the TET uses the device as theywould a normal telephone. The difference is that for a TET, in additionto the remote person's spoken voice being heard over the telephonespeaker or earpiece, the words spoken by the remote user appear inwritten text form on the visual display, where they can be read by theperson with hearing difficulty. Thus, to the person who is hearingimpaired, the use of the TET device is "normal," and in accord withtheir usual habit, and the person gains the benefit of any non-verbalspoken cues, such as inflection, volume, pauses, or the like, that theuser can hear, as well as receiving in a text character stream all ofthe words actually spoken by the other person.

The functioning of such a device will preferably be based on an enhancedTDD protocol, such as the one which will be disclosed below. It is to beunderstood, however, that TET can also be implemented in devicesoperating in conventional Baudot or other digital text data protocol,such as ASCII or CCITT. A TET device may also employ the existing relaysystem to serve as the communication link to convert oral to textcommunication, also as will be described below. Thus the specificationbelow will begin with a schematic of the prototypical TET device,followed by a description of the preferred code system, a description ofrelay operation in general, and then a description of several of thevariants of TET design which may be utilized within the system of thepresent invention.

The Text Enhanced Telephone

Shown in the schematic illustration of FIG. 1 is the circuitry of oneembodiment of a version of a text enhanced telephone (TET) operated inaccordance with the present invention. The TET device of FIG. 1 is adevice intended to be inserted in series in between the base unit of aconventional telephone and the wall jack into which the telephone isconnected. Therefore, at its input, and its output, the TET of FIG. 1 isconfigured to have conventional analog telephone connectors or jacks.Indicated at 12 is the jack which would be connected to the telephone,and indicated at 14 is the jack which would be connected to thetelephone wall jack. Connected to each of the respective input andoutput jacks 12 and 14 is a device referred to in the telephone industryas a hybrid or a two-wire to four-wire converter, the two hybrids beinglabeled 16 and 18 respectively. These hybrids, conventional in thetelephone and data communications industry, serve to either separate orcombine the transmitted and received analog telephone signals or, astheir other name implies, separate the two-wire telephone signal intofour wires. On the transmit line, which is created from the hybrid 16,the line is connected next to a notch filter 20. The notch filter 20, ofconventional design in the art, is specifically intended to pass signalsof all frequencies, except those at the digital text communicationfrequencies, which are 1400 and 1800 hertz for the enhanced TDD protocoldescribed below. The output of the notch filter 20 is connected throughan analog summer 24 to the input side of the hybrid 18. The output sideof the hybrid 18 is connected as an input to a notch filter 22, which issimilar in design to the notch filter 20, and also constructed toprovide filtering of signals at 1400 and 1800 hertz. The output of thenotch filter 22 goes as the input to the hybrid 16.

Also connected to the same line that goes to the input of the notchfilter 22 is a band pass filter 26. The band pass filter 26, also of adesign conventional within the art, is the converse of the notch filters20 and 22. The band pass filter 26 is intended to pass only signals at1400 and 1800 hertz. The output of the band pass filter 26 is connectedto a tone detect circuitry 28, or receive modem as they are also termed,of a type conventionally used in TDD devices. The tone detect circuity28 detects either 1400 or 1800 hertz, and provides an appropriatedigital output to a microcontroller 30. The microcontroller 30 includesa microprocessor and appropriate ROM and RAM memory. Code stored in theROM directs the operation of the microprocessor. On the output side ofthe microcontroller 30 is a digital to analog converter 32, the outputof which is connected as the other input to the analog summer 24. A DTMFdecode circuit, indicated at 34, is connected to the output line fromthe hybrid 16, and is the type of device intended to decode the dualtone multifrequency, or "Touch Tone," (Trademark) signals from a pushbutton telephone. The output of the DTMF decode circuit 34 is alsoconnected as an input to the microcontroller 30. The microcontroller 30also operates a normally closed switch, or relay, 35 located between thehybrid 16 and the notch filter 20 after the connection to the DTMFreceiver 34. A series of user accessible switches 36 are also connectedas inputs to the microcontroller 30. The microcontroller 30 is alsoconnected to a visual display 38 which is capable of providing analpha-numeric display of text characters presented to it by themicrocontroller 30. Separately, a bypass circuit, designated at 40, andcontrolled by an on/off switch 41, is connected between the input andoutput telephone jacks 12 and 14 directly and which, when actuated, iscapable of bypassing the entire internal components of the device ofFIG. 1.

The operation of the device will be described briefly here, and then inmore detail below. The purpose of the TET device, when enabled, is tointercept the outgoing call placed by the user, as detected by the DTMFdecode circuit. The microcontroller 30, during the dial by the user,intercepts the dialed tones and does not present them on the output lineby opening the switch 35. When the user has finished dialing the number,the microcontroller 30 utilizes its analog capabilities, accessedthrough the D to A converter 32, to present on the output line the DTMFsignal for a telephone number, but not the telephone number dialed bythe user. Instead, the microcontroller 30 dials the number of the TETrelay which the user normally utilizes. As the TET device makes initialcontact with the relay, the TET device passes to the relay a series ofmachine command codes. The operation of such command codes will bedescribed below. The function of the command codes at this point is toinform the relay as to the type of call to be implemented, and then topass to the relay the number for the ultimate hearing person to beconnected. The relay equipment will then automatically dial the numberof the hearing user and configure a TET relay with a call assistant inthe loop between the TET device, operated by the TET user, and thehearing user at the other end of the line.

When the set-up is completed, the hearing user speaks and the callassistant types the words spoken by the hearing user into the TDD at therelay. The telephone line between the TET and the relay will carry boththe spoken words of the hearing user and the digital signals for thetext typed into the device used by the relay call assistant. In the TETdevice of FIG. 1, the purpose of the notch filter 22 is to keep the textcommunication tones from being heard by the TET user. At the same time,the purpose of the notch filter 20 is to prevent the words spoken by theTET user from inadvertently interfering with the transmission andreceipt of the digital communication tones. While the communicationsession is on-going, the TDD tones are passed through the band passfilter 26 and detected and decoded by the microcontroller 30. Themicrocontroller 30 decodes the digital text, and then presents a textcharacter stream of the words spoken by the remote party on the visualdisplay 38 so it can be read by the user. Thus the user, without havingto take specific action, has created a call in which he or she may speaknormally to the person at the other end of the line, and the person atthe other end of the line may also speak normally. The hard of hearingor deaf user does not hear any of the digital communication tones forthe text, but sees at his or her TET device a visual text characterstream of the words spoken by the user at the other end of the line, ina real time fashion.

These advantages to the user, and the intimate functioning of the deviceof FIG. 1, can best be understood by understanding some additionaltechnical details of the device which will be described below.

TET Relay

As relays for the TDD community are presently constituted, the relayserves as a translator between Baudot or TDD users and users who canspeak and hear. The person employed at the relay, referred to as a callassistant, sits at a TDD terminal and wears a headset connected as aregular voice telephone. Using the TDD operated by the call assistant,the call assistant communicates in a digital code over one telephoneline to the TDD user, preferably using an enhanced TDD protocol. Usingthe headset, the call assistant communicates over the second telephoneline in normal voice with the speaking and hearing party. In this way,the deaf person is facilitated in communicating with hearing personsover the telephone. Such relays are now maintained by local or regionaltelephone exchanges all over the United States, and in other countries,and are specifically intended to allow access to the telephonecommunication system for users who have difficulty hearing or who cannothear.

One enhancement that has already been built into some relays is intendedto provide better telephone access to users who can speak but not hear.Such persons may still use a relay, but use it in a mode known as "voicebridge" or "voice carry-over" (VCO), where the voice of the deaf or hardof hearing user is transmitted through the relay to the hearing user.Such a voice bridge relay system is discussed and disclosed in moredetail in U.S. Pat. No. 5,081,673, the disclosure of which is herebyincorporated by reference. Shown in FIGS. 2, 3 and 4 are schematicallythe different arrangements of relay usage for normal relay, voice bridgerelay, and text enhanced telephony relay respectively. In each of FIGS.2, 3, and 4, the hearing and speaking user is at the telephone 42.

The telephone 42 of the hearing and speaking user is connected in FIG. 2to the handset (or headset) 43 of the call assistant who uses a TDD 44to communicate with the TDD 46 of the deaf or hard of hearing person.

In FIG. 3, the voice bridge, a switching circuit 48 connects thetelephone line from the telephone 42 to a telephone 50 accessed by thedeaf or hard of hearing user. The switching-circuit 48, such as thatdescribed in the above U.S. Pat. No. 5,081,673, connects the twotelephones 42 and 50 such that when voice is on the line and opens thecircuit when TDD signals are on the line, as when either of the TDDs 44or 46 are operated. Thus, the variant of FIG. 3 permits text or voice onthe same line, between the relay and the disabled user, alternately, butdoes not permit simultaneous transmission of text and voice. Also, sincethe telephone line between the relay and the telephone 50 is switched totext transmissions when the user at telephone 42 is speaking, voice isnever received at the telephone 50.

Illustrated in FIG. 4 is the general scheme for the typical relayimplementing TET. The telephone 42 of the hearing user is connected by afirst telephone line 45 to the handset 43 of the call assistant. Thecall assistant types at the TDD 44, placing data communications on asecond telephone line between the relay and the hard of hearing user whois at the telephone 50. A TET appliance 52 is also placed in series withthe telephone 50. A filter circuit 51 connects the telephone line 45from the hearing user's telephone 43 to the telephone line 47. Thefilter circuit 51 is constructed such that all voice communications, butno data signals from text, pass through the filter circuit 51, so thatthe hearing user does not hear the communication tones of the texttransmissions. At the station of the deaf or hard of hearing user, theTET appliance 52 receives the text communications from the TDD 44 anddisplays the received text characters for the user. At the same time,the TET device 52 filters from the telephone line 47 the textcommunications signals so that the user on telephone 50 only hears thevoice communications. Thus the users of the two telephones 42 and 50converse normally, with the communication to the user of the telephone50 assisted by the display of the text of what is said by the other useronto the visual display of the TET appliance 52.

Thus, to implement the present invention, some modifications must bemade to the configuration of the relay. A schematic diagram showing sucha modified relay for TET operation is shown in FIG. 5. In FIG. 5reference numerals are similar to FIG. 4 for similar parts, such as thecall assistant's headset 43, the TDD 44 of the call assistant and thefilter circuit 51, shown here in more detail. At each of its ends, therelay of FIG. 5 includes hybrids 54 and 56 to separate the singletelephone line carrying communications in each direction into separatelines for each direction. A notch filter 58 is connected to the hearinguser's telephone line 45. The notch filter 58 is, again, constructed soas to pass through signals of all frequencies, except for signals at thetext communications frequencies, preferably the 1400 and 1800 hertztones of enhanced TDD protocol. Also connected to the input line is aamplifier 63, connected to supply voice from the hearing user to theheadset 43 of the call assistant. A side-tone amplifier 62 is connectedto feed attenuated voice of the call assistant back to the callassistant for normal voice feedback purposes. The output of the notchfilter 58 passes through AGC amplifier 64 and an analog summer 66 to beconnected to the telephone line 47 to the TET user.

The telephone line 47 from the TET user, connected through the hybrid56, is passed through a notch filter 68, then through an AGC amplifier70 to the telephone line 45 to the hearing user. Also optionallyconnected to the telephone line 47 from the TET user is a band passfilter 72, constructed so as to pass only the digital communicationfrequencies. The output of the band pass filter goes to the TDD 44,while the output of the TDD 44 is connected through the analog summer 66to the TET user's telephone line 47.

The circuit of FIG. 5 thus permits both voice and text to be carriedsimultaneously on the telephone line 47 between the TET relay and theTET user. The text communication frequencies are filtered out by thenotch filter 68, so that the hearing user and the call assistant willnot hear the text communication tones. Meanwhile, voice signals passthrough the relay in both directions.

The purpose of the notch filter 58 in the circuit of FIG. 5 is tominimize voice interference with accurate text communications. Sincenormal human voice may contain frequency components at 1400 and 1800hertz, the voice signal could garble the text communications between thecall assistant and the TET user. By using a narrow notch filter, littleor no voice content is perceived to be lost while the accuracy of texttransmission is maintained. If some garbling of text is acceptable, itmay be possible in some applications to omit the notch filter 58.Similarly, the band pass filter 72, inserted to assure the integrity oftext communications, if desired, to the call assistant, can be omittedif no such transmissions are to be conducted.

Certain optional functions of the TET device, when used in conjunctionwith the TET relay, are made possible by the use of the enhanced TDDprotocol and machine control codes. Thus these protocols will bedescribed next.

Enhanced TDD Protocol

To make use of the present invention, a code system is required whichpermits the transmission of text communications efficiently and quickly.The preferred system for use in the present invention is an enhanced TDDprotocol, specifically designed to be backwardly compatible with theinstalled base of Baudot TDD communication terminals. The enhanced TDDprotocol is based on frequency shift keying encoding an average, thoughvariable, transmission rate of just over 100 BAUD. The signals for alogical 1 and logical 0 in the enhanced TDD protocol are just as theyare in standard Baudot, i.e. 1400 hertz for a mark and 1800 hertz for aspace. However, the enhanced TDD protocol is unusual in that, forreasons having to do with the electronics associated With TDD tonerecognition circuitry, the time for a space bit and the time for a markbit are defined to be different. The space bit is defined to be 12milliseconds, while the mark bit is defined to be 7 milliseconds.Moveover, the enhanced TDD protocol character set consists of a 7 bit128 character table, such as the ASCII or CCITT character table, ratherthan the conventional 32 or 64 character table used by conventionalBaudot communications. This permits the enhanced TDD protocol to useupper and lower case letters, as well as leaving extra charactersavailable for machine control functions. The enhanced TDD character datasignal consists of a start bit, the 7 character bits, no parity bit, and2 stop bits. The start bit is a space and the stop bits are both marks.

The enhanced TDD protocol, like conventional Baudot protocol, operatesin a simplex mode, in which only one of the two terminals communicatingcan be transmitting at any one time. However, the details of operationof the enhanced TDD protocol result in a pseudo-duplex capability. Thepseudo-duplex capability arises because each of the enhanced TDDprotocol terminals is constrained by virtue of its programming tooperate in accordance with two rules. The first rule is that eachterminal is constrained not to make any transmissions outward on itscommunication line while it is receiving data. During the time periodthat the terminal is receiving data, characters entered from thekeyboard are not transmitted, but are stored in a buffer. The enhancedTDD protocol terminal will wait until there is a pause in thecommunication line before transmitting characters from its buffer inturn toward the other station. The second rule of pseudo-duplexcommunication requires that the enhanced TDD terminal pause after acertain N number of characters have been transmitted. The number ofcharacters N is between 1 and 72, and preferably between 1 and 20. Thus,only one station is transmitting at a time, and the other stationlistens and buffers characters until the first station pauses, at whichtime it begins transmission of characters. The effect of the operationof these two rules, together with the higher speed of transmissionachieved by communication at over 100 Baud, causes the communicationbetween the two stations to appear duplex to the users, even though onan electrical signal level, communication is simplex. It is for thisreason that this style of communication is referred to as pseudo-duplex.

In addition to the other differences from conventional Baudotcommunication, the enhanced TDD protocol requires a recognition orhandshake protocol in which the two stations must establish that theyare both capable of enhanced TDD protocol communication before switchingfrom conventional Baudot communications to the enhanced TDD protocol.Accordingly, the enhanced TDD protocol preferably includes a series ofsynch-originate characters and synch-answer characters, which aredefined not to be printing characters, which the stations may transmitto each other to identify themselves to each other and to switch intoenhanced TDD protocol communication. The synchronization characters alsohave non-standard bit times so they can be distinguished fromdisplayable characters. To originate communications, an originatingspecial synchronization character, referred to as the "O-synch" sequenceis transmitted by the calling station. If the called enhanced TDD devicereceives and recognizes the O-synch sequence, and is capable of enhancedTDD communication, then it transmits an "A-synch," or answersynchronization sequence, to the originating station. FIG. 6 illustratesan exemplary O-synch sequence at 74 and an exemplary A-synch sequence at76. After recognizing the transmission and receipt of these signals bothmachines can then communicate in the enhanced TDD protocol. If theenhanced TDD terminal fails to receive proper synchronization sequencefrom the remote unit, it assumes that the remote unit is operating inconventional Baudot protocol, and continues all communication using theconventional Baudot protocol.

Machine Control Commands

The enhanced TDD protocol described above makes use of the larger 7 bitcharacter set. Unlike the smaller 32 character Baudot character set, the7 bit ASCII and CCITT character sets of 128 characters include bothupper and lower cases as well as a full set of punctuation characters,and also includes the capability to include control characters. Thispermits the enhanced TDD to operate with control codes not presentlyavailable in conventional Baudot communications. Such control codes maybe used to facilitate machine-to-machine communication along the sametelephone lines used for communication between the users of the TDDdevices, but in a manner invisible to the users of the TDD terminals.

Of particular interest, and with relevance to the present invention, aremachine-to-machine commands for controlling and sending information to aTET relay station. In particular, the TET device, utilizing machinecontrol commands transparent to the user, can configure the relay to amethod of communication which is suited to the type of call that theoriginating station wishes to make, i.e. to set itself up for TETcommunications. The type of set ups will be described below after themethod of implementing machine control commands is described first.

A preferred system for machine control commands begins through the useof special synchronization sequence which is similar to the O-synch andA-synch, as described above. The special synchronization sequence,indicating a machine command is to follow, is here termed the REQ!(request) sequence. The purpose of the REQ sequence is to indicate thatmachine command codes follow but to avoid requiring the user to waitwhile a lengthy character set is transmitted to initiatemachine-to-machine communication. A form of REQ! signal is indicated atin FIG. 6.

The protocol for machine-to-machine messages under the enhanced TDDprotocol follows the following format:

     REQ!  CATEGORY!  FUNCTION!  ERQ!

In a command of the format described above, REQ! is the synchronizationsignal described above which is defined to be a non-printing characterwhich is detectable by both the originating and receiving machinesoperating under the enhanced TDD protocol. The characters should beselected so as to be non-printing and non-recognizable on a conventionalBaudot TDD device.

As illustrated in FIG. 6, the REQ! sequence begins with an echosuppression pulse "EST" for 35 milliseconds to unlock the receivingphase locked loops. This is followed by three 18 milliseconds mark tonesand two 24 milliseconds mark tones, each separated by twelvemilliseconds of echo suppression tones. The pattern is terminated with a35 millisecond echo suppression pulse. The REQ! sequence isdistinguishable from the A-SYNCH sequence by the length of the final twomark tones.

The REQ! sequence is not an ASCII character, both because it does notconform to the format of an ASCII character with start and stop bitsflanking a sequence of marks and spaces, and because it is not one ofthe character codes obtainable with the ASCII word length. It follows,generally, that the REQ! sequence may not be initiated by the TDD userby pressing the keys on the keyboard. For this reason, the REQ! sequenceis particularly well suited for applications, such as initiating the"downloading" of emergency information by an emergency service, whichshould be reserved to particular users, such as legitimate emergencyservices.

The REQ! sequence is followed by a CATEGORY! character which is a 7 bitbinary number limited to 16 numbers from hexadecimal 10H (16) to 1FH(31). These are nonprinting characters under the ASCII character set andthus provide a degree of error correction without risk of printing onthe TDD. If the character following the REQ! sequence is not within the10H to 1FH range then the machine-to-machine communication procedure isaborted before it causes a response or changes operation of the TDD.

In the preferred embodiment, CATEGORY! 10H is reserved for generalmachine-to-machine communication between TDDs, whereas CATEGORY! 11H isused for automatic machine-to-machine communication for emergencyservices. CATEGORY! 12H is used for machine-to-machine communication forTDD or TET relay functions.

The next character of the machine-to-machine message format is aFUNCTION! character which may be any 7 bit number. The value of theFUNCTION! character is interpreted in light of the CATEGORY! characterpreviously transmitted. If the CATEGORY! character is 11H (emergencyservices), then a FUNCTION! of 01H instructs the originating TDD totransmit caller information in a block format as will be describedbelow. The pseudo-duplex capabilities of the enhanced TDD protocoleliminates the possibility that this block of information will beinadvertently interrupted and garbled by transmissions by either party.If the CATEGORY! value is 12H (relay services), FUNCTIONS! 01H to 06Hmay be obtained as provided in Table I.

                  TABLE I                                                         ______________________________________                                        01H           Number to dial                                                  02H           Carrier of choice                                               03H           Relay user ID                                                   05H           VCO on                                                          06H           VCO off                                                         07H           TET on                                                          07H           TED off                                                         09H           Transmit relay information block                                ______________________________________                                    

"Number to dial" is the number of the other party of the conversation,which in this manner may be received and dialed automatically by therelay without operator intervention to eliminate the possibility oferror in dialing, to speed the dialing process, and to enhance theprivacy of the communication.

FUNCTION! 03H, the relay user ID is a personal identification numberthat may be requested of the originating caller to check forauthorization of a particular user to use the relay whereas FUNCTION!04H and FUNCTION! 05H: "VCO On" and "VCO Off" control a TDD voice bridgeas described above.

For TET relay use, two machine commands may be used. The first might bea FUNCTION! 01H, directing the relay to dial a remote hearing user toinitiate communications. The second might be a FUNCTION! 06H, tellingthe relay to set up for a TET configuration, such as is shown in FIG. 5.

The final portion of the machine-to-machine message format is an ERQ!(end of request) character which is a standard ASCII character 04H. Thetermination of the machine command by the ERQ! character is used toallow the TDD software to respond to machine-to-machine requests atvariable lengths. For example, the response to a request for emergencyservice caller information could be any length from zero (no data) totens of characters. The initiating TDD would collect the charactersuntil an ERQ! character was received. The format for a response to amachine-to-machine request is simply

     REQ!  RESPONSE!  ERQ!

where RESPONSE! is the responding data.

Thus these command functions, and the use of the enhanced TDD protocolenable both the TET device and the relay to automatically properly setup a call for the user. The enhanced TDD protocol devices are capable ofunderstanding their respective roles in the TET relay system and actingaccordingly. Thus, for example, the TDD 44 of the call assistant mayreceive command codes from the TET appliance of the TET user instructingit to dial another party and automatically engage the relay in a TETconfiguration.

Other command characters could select other parameters of TET relayfunction. One could be two-directional TET. Another might select voiceprivacy or a male or female call assistant. Text protocols, codeselections and similar technical parameters can be selected by thesecommands. Thus the user education and participation are minimized.

Circuit Details and TET System Variations

Thus, it can be appreciated from the above discussion that the textenhanced telephone system and devices of the present invention differfrom prior devices in that the same telephone line is used to carryvoice and, at the same time, a digital signal representing a textcommunication containing the words in text that are being spokensimultaneously by voice. At each end of the telephone line which carriesboth the text and voice communications, care must be taken to filter thedigital communication frequencies from the earpieces of the users andalso to filter from the voice signals of each of the users any signalsat those text communication frequencies which might otherwise interferewith the text communications. Thus the use of notch filters is importantto the present invention. Shown in FIGS. 7 and 8 are two embodiments ofexemplary high performance notch filters which may be used within thepresent invention. Many other designs are, of course, possible as well.

Referring first to FIG. 7, which shows a type of notch filter known intext books as "Twin-T," the input signal 80 is connected through a pairof resistors 82 and 84 to the input of an integrated circuit voltagefollower. The input signal 80 is connected through a capacitor 88 toground and the junction of the resistors 82 and 84 is connected throughthe series of a capacitor 90 and resistor 94 to ground, with thejunction of the capacitor 90 and the resistor 94 also connected to theinverting input of the voltage follower 86. The output of the voltagefollower 86 is connected through resistors 96 and 98 to the input of asecond integrated circuit voltage follower designated 100. Capacitors102, 104, 108 and resistor 106 are connected similarly as to thecorresponding components associated with the voltage follower 86. Thevoltage follower may be any of a wide number of integrated circuitsdesigned for this purpose, such as a National Semiconductor LM102. Thevoltage follower 86 and the voltage follower 100 operate as notchfilters, with the frequency of the notch being determined by theappropriate selection of resistors and capacitors associated with eachof the integrated circuits. By appropriate choice of resistor andcapacitor combinations, it is possible to use the circuit of FIG. 7 toselectively notch filter exactly 1400 and 1800 hertz from a broad bandcommunication signal.

Similarly, shown in FIG. 8, an input signal 80 is connected as one inputto a universal dual filter building block integrated circuit 110. Thefilter building block integrated circuit also receives a clock pulse oninput line 111. The frequency of the clock pulse on line 111 determinesthe frequency at which the integrated circuit 110 performs filteringoperations. The output of the integrated circuit 110 is connectedthrough a buffering amplifier 112 to the input of a second universaldual filter building block integrated circuit designated 114 which alsois driven by an appropriate clock signal 116. The output of theintegrated circuit 114 is connected through a buffer 118 to the outputsignal 120. If the input line 111 to the integrated circuit 110 isoperated at 140,000 hertz and the clock signal 116 to the integratedcircuit 114 is operated at 180,000 hertz, the series combination ofthese two integrated circuits will create a dual notch filter filteringout from the input signal a notch of frequencies centered on 1400 and1800 hertz respectively. A suitable integrated circuit for use as thebuilding block integrated circuits 110 and 114 is the Linear TechnologyLTC 106 or other similar integrated circuit.

Among the other ways that text signals can be separated from voice, oneother merits particular mention. It is possible to digitize the entiretelephone signal incorporating both voice and text signals. Then it ispossible to manipulate that digital signal using a digital signalprocessing (DSP) integrated circuit, of which many are commerciallyavailable. Using the DSP, a digital filtering of the tones representingthe frequencies of the text communication can be done mathematicallywith high precision. After processing, the DSP output is again convertedto analog form for presentation to the user.

Another variant possible within the present invention, although perhapsa less desirable one, would be to construct a TET circuit, similar toFIG. 1, but without the hybrid circuits. Using a single telephone line,which carries signals both directions, notch filtering would still benecessary to prevent text communications from reaching the ear of theuser. This device might also use switching of the telephone line inresponse to sensed signal type (i.e. local voice versus received voiceand text) to prevent input text signals from reaching the user's ear.

In FIG. 1 above, it was specifically envisioned that the text enhancedtelephone communication appliance was inserted in series in between thetelephone base station unit and the wall jack to which the telephone wasto be connected. While it is important to the present invention that theTET device be capable of receiving both digital communications and voicecommunications over the common telephone line, there are severalphysical configurations in which a TET device can be configured so as tooperate with, or replace, the conventional telephone. For example, shownin FIG. 9 is another embodiment. In the embodiment illustrated in FIG.9, the TET appliance is placed in series between the handset of aconventional telephone and the base unit. The TET of FIG. 9 will notfunction to intercept and dial on behalf of the user, so dialing of theTET relay must be manually by the user, but other than that difference,the device of FIG. 9 functions in a manner quite similar to the TETdevice of FIG. 1. In fact, those components in the embodiment of FIG. 9which are identical in their connection and function to thecorresponding components in the embodiment of FIG. 1 have been givenidentical reference numerals, and will not be described in additionaldetail herein.

Referring in detail to FIG. 9, the telephone handset 121 is connectedthrough a conventional jack 122. Since the connection between thetelephone base unit and the handset is conventionally a four-wireconnection, no hybrid circuit is required. The connector or jack at theother end of the device, designated 124, is intended to connect to thetelephone base unit 123.

The device of FIG. 9 is particularly intended to function as a receiveTET device and to automatically commence operation when digitalelectronic communications are received over the incoming telephone line.Accordingly, there is an automatic voltage detect circuit created usingthe operational amplifier 126. This amplifier is constructed so as todetect when a signal of any kind is received over the incoming telephoneline to the handset. The output of the operational amplifier 126 isconnected to a buffer 128 which serves to turn the power on and off tothe microcontroller 30. Connected in series between the notch filter 22,which is placed on the incoming signal line is a volume, and controlcircuit 130 which allows the volume and the handset to be adjustedaccording to the user's desires.

Again, the in line TET device of FIG. 9 operates in a fashion exactlyanalogous to the operation of the TET device of FIG. 1, except that itis placed in between the handset and the base station rather thanbetween the base station and the wall jack of the telephone. Thisembodiment does not intercept the dialing on behalf of the user, but ifthe user is willing to dial the relay manually, the circuit of FIG. 9will satisfactorily and adequately perform text enhanced telephoniccommunications, prevent digital communications from being heard by user,and display any digital communication signals received so that they canbe read by user in exactly the same fashion as the circuit of FIG. 1.

It is also specifically envisioned herein that rather than building aseparate appliance which is placed between the handset and the base unitor between the base unit and the telephone jack, the circuitry for theTET device can actually be constructed inside the telephone itself in asingle unitary appliance. The external appearance of such a device isshown in FIG. 10. This device incorporates the circuitry of FIG. 1within the housing in which the telephone is manufactured. The onlychange necessary to the telephone exterior would be the need to providefor a display, so that the digital display 38 can be seen by the users,and the need to provide some place for a few controlling buttons 36 and40 to turn on and turn off or otherwise select the function of the TETfunction. However, note that this device also includes a keyboard,connected to the microcontroller, So that it can also be used as aconventional TDD (send as well as receive) by users who need thatfunction as well.

It is preferred, as described above, that the digital communicationfrequencies of the present invention be the Baudot tones which are usedin the enhanced TDD protocol described above. The main reason fordesiring the use of these Baudot tones, is that so the devices can becompatible with other TDD and Baudot communicating terminals and relays.However, it is also envisioned herein that rather than using Baudottones, that the digital communications in accordance with the TETdevices of the present invention could actually be conducted in otherdigital communication protocols, notably the ASCII or CCITT toneprotocols conventionally used by digital computers. The only differencesin the embodiments described herein which would be required through theuse of ASCII or CCITT, rather than Baudot tones, is that the notchfilters would have to be constructed so as to filter at the frequenciesof the ASCII or CCITT carrier tones, rather than at the 1400 and 1800hertz signals used by both Baudot and enhanced TDD communicationprotocols.

It is specifically envisioned that on occasions it may be desirable toconnect two, or more, TET users through a TET relay such that both usersmay obtain the benefits of text enhanced telecommunications. Shown inFIGS. 11 and 12 are two set ups by which that objective can beaccomplished. In the system of FIG. 11, in which parts similar to therelay of FIG. 5 have been provided with similar reference numerals, thesystem is set up to utilize a pair of call assistants, one dedicated totranscribe the voice of each of the two TET users. One of the callassistants utilizes the TDD 44A and the telephone 43A while the otherutilizes the TDD 44B and the telephone 43B. Between the hybrids 56 and54, two oppositely oriented, and identical, circuits are providedanalogous to the circuit on one side of the TET relay of FIG. 5. Thereceived telephone signal goes through an AGC amplifier 64 and thenthrough a notch filter 58 to separate out voice components which mightinterfere with data. The voice is fed to the telephone 43A or 43B forthe respective call assistant and also to a summer 66 where it is summedwith the output of the respective TDD 44A or 44B. The system iscompletely symmetrical. Thus, between each hybrid and the respectiveuser, the telephone line carries simultaneously the voice of the otheruser and a text communication which represents the simultaneoustranscription of what is said by the user at the other end of thetelephone. The text communications between the two users do notinterfere with the voice communications between the users since, on eachside of the relay indicated in FIG. 11, the text is only transmitted tothe user who desires to see that text and the text and voice arecarefully filtered from each other. Again, as far as each user isconcerned, they utilize their normal telephone mannerisms and habits.The difference is that as each user talks, the other user sees shortlythereafter a visual indication of the text of what the speaker hasspoken on the visual display on his TET appliance.

Shown in FIG. 12 is yet another embodiment illustrating how a two wayTET relay could be constructed utilizing a single operator. In thisinstance, the output of both telephones is connected through a summer141 to the telephone 43 of the operator. A switch 144 is used either toallow both parties to see the text of either transmissions or,alternately, the switch 144 can be constructed so as to be toggled bythe operator so that each party only receives the text version of thewords spoken by the opposite party.

It is specifically contemplated herein that technological developmentsover time will enable the function of the call assistant to be, at somepoint in the future, an automated function. Once computer assisted voicerecognition systems become practical such that they do not requiretraining with a particular voice, the call assistant in any of the relayconfigurations described above could be replaced by an automatedcomputer. The computer would be programmed simply to translate into textthe words spoken by the user and to pass the text to the TET user in afashion similar to that described above. The only difference is incircuitry would be that the human being representing the call assistant,and that person's telephone and TDD, would be replaced by an automatedvoice recognition digital electronic system.

It is also envisioned that there may be uses for the TET technologydescribed herein for situations other than the hard of hearing user. Forexample, such a TET relay system could be utilized for translationswhere a party understands a foreign language, but only partially. Byarranging to have a TET relay operator who was capable of providing asimultaneous translation, a user could arrange to have telephoniccommunications with a remote user who speaks a language the TET userpoorly understands. In that instance, the call assistant wouldsimultaneously translate and type and the TET user could see on his orher display his own native language translation of the words beingspoken by the remote user. A TET relay and appliance system may also bedesirable in situations where it is desired to record telephonicconversations. It is a simple matter to attach a printer to a TETappliance of the types described above. With such a TET appliance, andutilizing a TET relay as described above, transcriptions of telephonecalls could be readily captured and printed in hard copy or stored on amagnetic or other storage medium. This might be particularly useful forconference calls, for business meetings or the like where transcriptionsof spoken words are desired. The service could also be used to createtranscriptions or text by a single user.

It is to be envisioned that the present invention is not limited to theembodiments described and illustrated herein, but embraces all suchmodified forms thereof as come within the scope of the following claims.

We claim:
 1. A text enhanced telephone station for use by a user who canspeak but has attenuated hearing, the station capable of receiving bothvoice and text communications simultaneously over one telephone line,the text communications transmitted using two digital communicationtones, the station comprising:a telephone hand set including a speakerand a microphone; a connector adapted to be connected to the onetelephone line; input wiring connected to carry input signals from theconnector to the speaker; output wiring connected to carry outputsignals from the microphone to the connector; a notch filter constructedto preferentially obstruct the two digital communication tones frompassing through the notch filter, the notch filter being connected inthe input wiring to filter signals to the speaker so that the digitalcommunications tones are not passed to the speaker; a modem connected tothe input wiring before the notch filter to convert any textcommunication at the digital communication tones to digital signals; amicrocontroller connected to receive the digital signals from the modemand to identify any characters encoded in the digital signals; and avisually readable display to display the characters identified by themicrocontroller, the microcontroller programmed to display on thedisplay the characters as they are received so that text communicationsreceived by the station are displayed to be read by a user; the stationbeing capable of both transmitting and receiving voice signals to orfrom the one telephone line simultaneously as it receives and displaystext communications over the one telephone line, without the digitalcommunication tones being audible to the user.
 2. A text enhancedtelephone as claimed in claim 1 wherein the digital communication tonesare 1400 and 1800 hertz.
 3. A text enhanced telephone as claimed inclaim 1 wherein the microprocessor is programmed, when asked to initiatea call by the user to another party, to (i) receive a telephone numberdialed by the user for the other party, (ii) dial and connect to a textenhanced telephone relay instead of the telephone number dialed by theuser, and (iii) send to the relay machine control functions in anenhanced TDD protocol which directs the relay to dial the telephonenumber dialed by the user and initiate text enhanced relaycommunications between the user and the other party.
 4. A text enhancedtelephone as claimed in claim 3 wherein there is further a plurality ofuser accessible switches to switch the microprocessor between a mode ofoperation where the telephone dials any telephone number dialed by theuser and a mode of operation where the microprocessor dials the textenhanced telephone relay.
 5. A text enhanced telephone as claimed inclaim 1 wherein there is a second notch filter on the output wiring tofilter from voice sounds of the user any tones at the digitalcommunication tones.
 6. A text enhanced telephone as claimed in claim 1wherein there is a band pass filter connecting the modem to the inputwiring to pass only the digital communication tones to the modem.
 7. Atext enhanced telephone communication device adapted to being connectedin series between a conventional telephone and a telephone line topermit both voice and text communications to be carried on a commontelephone line, the text communications carried at digital communicationfrequencies, the device comprising:a first connector to connect to thetelephone; a second connector to connect to the telephone line; twohybrids to separate telephone signals outbound from the telephone fromtelephone signals inbound to the telephone; a notch filter connected toa one of the hybrids to receive the inbound telephone signals andconnected to filter out any digital communications frequencies toprevent passage of text communications to the telephone; a decodingcircuit connected to the hybrid to receive the inbound telephone signalsbefore the notch filter to decode the text communications from thedigital communications frequencies; a visual display; and amicrocontroller connected to the decoding circuit programmed to decodetext characters in the text communications and to promptly display thecharacters on the visual display as the characters are received, whereinthe device can receive both voice and text communications on the commontelephone line with voice passing to the user while the textcommunications are used to create a visual text character stream forreading.
 8. A text enhanced telephone as claimed in claim 7 wherein thedigital communication frequencies are 1400 and 1800 hertz.
 9. A textenhanced telephone device as claimed in claim 7 wherein themicrocontroller is programmed, when asked to initiate a call by a userto another party, to (i) receive a telephone number dialed by the userfor the other party, (ii) dial and connect to a text enhanced telephonerelay instead of the telephone number dialed by the user, (iii) send tothe relay machine control functions in an enhanced TDD protocol whichdirect the relay to dial the telephone number dialed by the user andinitiate text enhanced relay communications between the user and theother party.
 10. A text enhanced telephone device as claimed in claim 9wherein there is a user accessible switch to switch the microcontrollerbetween a mode of operation where the telephone dials any telephonenumber dialed by the user and a mode of operation where themicroprocessor dials the text enhanced telephone relay.
 11. A textenhanced telephone device as claimed in claim 7 wherein the device alsoincludes a dual tone multifrequency receiver to receive and decodedialing by a user.
 12. A text enhanced telephone device as claimed inclaim 7 wherein there is a second notch filter connected to the hybridcarrying the telephone signal outbound from the telephone to filter outany voice components at the digital communications frequencies.
 13. Atext enhanced telephone device as claimed in claim 7 wherein there is aband pass filter connecting the decoding circuit to the hybrid carryingthe telephone signals inbound to the telephone to pass only signals atthe digital communications frequency to the decoding circuit.
 14. A textenhanced telephone communication device adapted to being connected inseries between a conventional telephone handset and a telephone baseunit of a telephone, and adapted to permit both voice and textcommunications carried at digital communications frequencies to becarried on a common telephone line connected to the telephone, thedevice comprising:a first connector to connect to the telephone handset;a second connector to connect to the telephone base unit, the first andsecond connectors being connected by inbound and outbound telephonewires; a notch filter connected in the inbound telephone wire to filterout any digital communications frequencies from transmission to thetelephone handset; a decoding circuit also connected to the inboundtelephone wire to decode the text communications from the digitalcommunications frequencies; a visual display; a microcontrollerconnected to the output of the decoding circuit and the visual displayand programmed to decode text characters in the text communications andto promptly display text characters on the visual display as textcharacters are received, wherein the device can receive both voice andsimultaneous text communications on the common telephone line with thevoice passing to a user while the text communications are used to createa simultaneous visual text character stream.
 15. A text enhancedtelephone device as claimed in claim 14 wherein the digitalcommunication frequencies are 1400 and 1800 hertz.
 16. A text enhancedtelephone device as claimed in claim 14 further including a notch filterconnected in the outbound telephone wire to prevent a user's voice frominterfering with the text communications.
 17. A text enhanced telephonedevice as claimed in claim 14 further including a band pass filterconnecting the decoding circuit to the inbound telephone wire so as topresent only the digital communications frequencies to the decodingcircuit.
 18. A text enhanced telephone station for communicating in bothvoice and text characters over a common telephone line, the textcharacters being transmitted at two discrete digital communicationfrequencies, the station comprisinga telephone handset including aspeaker and a microphone; a notch filter connected to the speaker toprevent passage to the speaker of both of the digital communicationfrequencies; a decoding circuit connected to the common telephone lineand responsive to signals at the digital communications frequenciesreceived over the common telephone line to convert those signals todigital signals; an analog output circuit connected to the commontelephone line to convert digital information into signals at the twodigital communications frequencies; a visually readable display; and amicroprocessor connected to the decoding circuit and the analog outputcircuit and the display, the microprocessor programmed to display textcharacters received in digital form from the decoding circuit on thedisplay so that a user can hear a voice and also see the text charactersof words that are spoken, the microprocessor also being programmed to,if a user indicates that a text enhanced call is to be originated, totransmit on the common telephone line a series of command codes causinga relay to be connected as well as the called party, so that the relaycan supply text characters of words spoken by a called party fordisplay.
 19. A text enhanced telephone station as claimed in claim 18wherein there is also a notch filter connected to the microphone so thata user's voice is filtered at the digital communications frequencies toprevent interference with the text communications.
 20. A text enhancedtelephone as claimed in claim 18 wherein the microprocessor indicatesthat a text enhanced call is to be made by communicating with the relayin an enhanced TDD communication protocol that permits command functionsto be transmitted to the relay.
 21. A text enhanced telephone as claimedin claim 20 wherein the enhanced TDD communication protocol operates atthe digital communications frequencies of 1400 and 1800 hertz.
 22. Amethod for text enhancing telephone communications over one telephoneline between a first telephone user who is hard of hearing or is deafbut can speak understandably and a second telephone user who can speakand hear spoken words, the method comprising the steps ofconnectingbetween the first and the second users a relay including speech todigital communications conversion capability such that text of thespoken words of the second user are transmitted at digitalcommunications frequencies on the one telephone line to the first userat the same time as the spoken words of the second user are transmittedover the one telephone line, at a telephone of the first user, filteringincoming telephone signals to a speaker of the first user so that thefrequencies of digital communications are eliminated from the speaker;and at the telephone of the first user, simultaneously translating thedigital communication frequencies received to text and displaying thetext in visually readable form so that the first user receives both thespoken words of the second user as well as a text transcription of thespoken words of the second user.
 23. A method as claimed in claim 22wherein the digital communications conversion capability includes ahuman call assistant connected telephonically to the second user whoenters words spoken by the second user into a digital communicationsterminal which places a digital form of the words in digitalcommunications frequencies on the one telephone line to the first user.24. A method as claimed in claim 22 further comprising the step of atthe telephone of the first user and at the relay filtering the telephonelines carrying voice to remove from voice any frequency components atthe digital communications frequencies so that the voice does notinterfere with the digital communications.
 25. A method as claimed inclaim 24 wherein the digital communications frequencies are 1400 and1800 hertz.
 26. A method as claimed in claim 22 further comprising thestep of the first user initiating dialing of a number into a telephoneconnected to a text enhanced telephone device, the text enhancedtelephone device intercepting the dialed number and dialing instead arelay, the text enhanced telephone device then transmitting commandcodes to the relay instructing the relay to dial the number dialed bythe first user and to initiate text enhanced communications through therelay with the dialed number.
 27. A text enhanced telephone station toallow a user to communicate in both voice and text characters over acommon telephone line, the text characters being transmitted at digitalcommunication frequencies, the station comprising:a speaker connected tobroadcast voice received over the common telephone line; a microphone totransmit voice of the user over the common telephone line; a filterconnected between the common telephone line and the speaker to preventthe digital communication frequencies from being broadcast by thespeaker; a decoding circuit also connected to the common telephone lineresponsive to signals at the digital communication frequencies to decodethe digital communication frequencies; a visual display; and amicroprocessor connected to the decoding circuit programmed to receivethe text characters and to display the text characters on the visualdisplay so that the user may simultaneously perceive both voice andvisually display text characters.